On a beach you can find a variety of substances ranging from clay, through sand, small and larger pebbles, stones and rocks. What you find on any beach is the result of a whole lot of factors.

A very important factor is erosion. The sea is constantly eroding land away from the shore all over the world – you can see this if you look at houses near the beach which often lose land or even become uninhabitable as the sea encroaches. You might expect that the more powerful the eroding force of the sea, the smaller the particles left on the beach (ie, in areas where the wave energy is less strong, you would find fine sand where the rocks have been worn almost to powder by the waves). In fact, it doesn’t work like that: very powerful waves eventually wash away fine, light particles such as sand particles, so it is only the larger ones that are left – pebbles or stones, for instance.

So a sandy beach is often a sign that the waves are less strong in that area. This even applies to different sections of the same beach. For example, if you walk along a sandy beach without shoes, as you get closer to the point where the waves break you may find that the sand starts to feel coarser. If you walk in the water and stand where the waves actually break (if the water is shallow enough for you to stand, of course) you should certainly feel this. What this means is that here the waves pound the shore with more force than they do elsewhere, and so the finer sand gets washed away and the larger grains remain. If you don’t find this difference even in the water, you are probably on a beach where the wave action is much less powerful than in other places.

You can also see this if you look at an area of very low wave energy, like an estuary, where the river flows down into the sea. In an estuary area you will tend to see particles that are even smaller than sand, like mud or silt – on most shorelines these would be washed away.

This can mean that sandy beaches are often safer for swimmers as the waves and current are less strong – but don’t count on it; sandy beaches can be dangerous too. You can find a list of safe sandy beaches here.

Another factor to consider is that sand is usually formed from stone that was softer in the first place, and so where you find sand, pebbles, stones, rocks etc close together it is likely that they were all formed from different types of rock. Over time many different types of rock may break down into sand, but it will take much longer in some cases than others. Most of the sand that we see on the beach is formed from silica in the form of quartz. Another common element in sand is calcium carbonate, which is found in most rocks but actually originates in the shells of all sorts of sea creatures as well as eggshells and other land organisms.  This takes hundreds of millions of years to form and it is this type of sand that is mostly found in coral reefs, for instance.

A good place to observe how the sea waves and the position of an area can effect the formation of sand and other particles is the Chesil Bank in south-west England. On this stretch of coast you will find a great variety of materials from sand and tiny pebbles at West Bay to large round stones at Portland. You can learn more about how these are formed here.